A Structural Description and Reclassification of the Wolf, Canis lupus,

Chorus Howl

by

Tanya D. Holt

Submitted in partial fulfillment of the requirements

for the degree of Master of Science

Dalhousie University

Halifax, Nova Scotia

October, 1998

O Copyright by Tanya D. Holt, 1998

Acquisions and Acquisitions et Bibliograph'c SeMcas services bibliographiques

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TABLE OF CONTENTS

Table of contents

Lkt of Tables

vii List of Figures

viii Abstract

Acknowledgments

Introduction

The Classification of Animal Vocalizations

Wolf Social Organization and Behavior

Wolf Vocalizations

a. Barks b. Growls c. Squeaks d. Howls

Rationale of Present Study

Methods

General Description

Study Sites/ Su bjects

a. Wolf Park b. international Wolf Center c. Wolf Education and Research Center

Stimulus Creation

Playback Experiment Procedures

Data Analysis- Acoustic

Data Analysis- Behavioral

Results

Composition of the Chams Howl

Properties of Chorus Vocal Types

a, Howls b. Squeaks c. Barks, Bark-howls and Growls

Structural C haracteristics of Choruses

Effect of Stimuli on Chomses

Behavioral Characteristics of Choruses

Discussion

Sumrnary of Major Findings

Choruses, Structure and Behavior

Vocal Composition of Choruses

Effectiveness of Stimuli

Vocal Mimicry

Conclusions

Directions of Future Research

Appendix

References

LIST OF TABLES

Table 1. The structure of the study pack ai Wolf Park. August 1995.

Table 2. The structure of the study pack at the International Wolf Center. October 1995.

Table 3. The structure of the study pack at the Wolf Education and Research Center, December 1995.

Table 4. Description of the stimuli used for the playback expenment.

Table 5. Structural characteristics of the bark, growl. squeak, howl and bark-howl vocal types.

Table 6. Cornparison of the published values for frequency and duration for the howl, squeak, bark and growl. to the wrresponding values observed in this study.

LIST OF FIGURES

Figure 1 . Spectmgraphic representation (stylized) of characteristic forms of the bark, growl. squeak. howl and bark-howl vocal types.

Figure 2. Spectrographs of A) the beginning, B) mid section and C) the end of a chorus vocalkation. showing the variability of vocal types contained within.

Figure 3. Vocal type composition (%) of each chorus recorded at Wolf Park.

Figure 4. Vocal type composition (%) of each chonis recorded at the International Wolf Center,

Figure 5. Vocal type composition (%) of each chorus recorded at the Wolf Education and Research Center.

Figure 6. Spectrograph of A) solo howl, B) breaking-howl and C) woa-woa howl.

Figure 7. Sequence of photographs showing the position of the head and mouth of a wolf uttering a woa-woa howl.

Figure 8. Spectrograph of squeaks contained within a chonis.

Figure 9. A) Spectrograph of a train of barks contained within a chorus. B) Spectrograph of a bark-howl uttered during a chorus. C) Spectrograph of a growl uttered during a chorus.

Figure 10. Duration and CoFM for chorus responses to each stimulus.

Figure 11. Photograph showing the alpha male and a subdominant male during a natural chorus. The alpha male remains lying down while howling.

vii

ABSTRACT

The wolf (Canis lupus) group vocalization referred to as the chorus

howl has historically been described as a f o m of howl, whereby two or

more pack members vocalize together. A playback experiment. using

arüficially created human howl imitations, elicited vocal responses from

three captive packs and provided evidence that chomses include not only

howls but also squeaks. barks. bark-howls and growls. In 17 choruses

recorded in this study, howls were the dominant vocal type in ternis of

overall number of vocalizations in the choruses (mean= 56 14%, n= .

1702). followed by squeaks (mean= 36 t 11%. n= 1202). barks (mean= 7 2

8%, n= 284). growls (mean= 0.6 t 1.2%, n = I l ) and bark-howls (n= 2). The

duration (s) and frequencies (Hz) of the vocal types contained within the

chofuses corresponded to previously reported values. This would indicate

that the information contained within the chorus may be a function of the

vocal composition. The data were also mildly suggestive of vocal mimicking

in wolves along a graded continuum of duration and frequency modulation.

From the observations made in this study it is recommended that the

vocalization know as the chorus howl be reclàssified as the "chorusn and

given its own category rather than being included in the howl vocal type.

viii

ACKNOWLEDGEMENTS

Many people have helped make this study possible. I would like to

thank my supervisor, Dr. Fred Hamngton, and the mernbers of my

supervisory cornmittee, Dr. John Fentress and Dr. Marty Leonard. for their

support and interest. In particular, I would like to thank J. Fentress for

welcoming me into his lab and providing al1 the space and equipment

required for data analysis.

At Wolf Park, I thank my human 'howlers', E. Klinghammer, P.

Goodman, M. Woodcock, M. Sloan and V. Kunch as well as A. Shaad, C.

Gardner, A. M. Shipper for providing both technical support and wonderhl

distractions.

1 am grateful to Dr. L. D. Mech. M. Nelson and the U. S. Geological

Survey- Biological Resources Division in Minnesota for providing me with

the opportunity to participate in their wolf project and for providing lodging

and more. at the Kawishiwi Field Station. Thanks also to M. Piotrow and

P. Wolf for assisting with data collection.

I extend sincere thanks to the management of the International

Wolf Center (W. Medwid and J. Templeton) and the Wolf Education and

Research Center for welcorning me to their facilities and answenng al1 my

varied questions.

On a persona1 level. 1 would like to express special thanks to rny

parents for providing al1 the cornforts of home and so much more. Thanks

also to Jeanne, Jennifer. the Capsticks. and the many fnends. old and

new. who provided encouragement. technical support. unconditional

friendship and 'play time'. I would like to thank the Holts (C.. B.. E. and J.)

at 'Holt's' for providing free coffee every rnorning for many years; thank

you. 1 am now an addict! Ifs with the deepest appreciaüon that I thank Pat

Harding for being a wonderful mentor and fiiend. Very speciai thanks to

Louis Blondin, for everything. always.

INTRODUCTION

The Classification of Animal Vocalizations

The classification of vocalizations has been the undertaking of many

researchers who study animal communication and behavior. The acoustic

parameters of animal vocalizations are measured in ternis of temporal

duration, and frequency (Hz) and amplitude modulation. Vocalizations that

have similar structural characteristics are then grouped together and referred

to as a vocal type. In theory, vocalizations that exhibit less within variability

than between variability when compared to other vocalizations make up these

vocal types. The vocal type names are often based on the sound itseif and

what it sounds like to the person doing the classification. For example, wolves

(Canis lupus) exhibit a vocal type referred to as the squeak (Crisler, 1958).

This high frequency, short duration vocal type sounds like the high plched

whine of a dog, yet, it was called the squeak. Some authors however cal1 this

vocal type the whine (Schassburger, 1987). This has caused some confusion.

It is of vital importance that authors use the same terminology to describe the

same vocal types for a particular species. The use of similar or the same

words to describe the vocal types of different species also occurs. For

example, red howler monkeys, Alouatta seniculus, (Sekulic, 1 982) and lions,

Panthera leo (McComb et. al., 1994) both roar to advertise territory

ownership. Classlication generally follows structural, contextual and

functional descriptions. To effectively classify animal sounds these sounds

must first be organized according to acoustic (structural) properties, then they

must be linked to associated behaviors to give a comprehensive description

of the animal's vocal repertoire.

The more we know about the type of vocalizations a certain organism

uses and the behavioral contexts under which each vocal type is observed,

the more we'll understand the types of information (something an animal

receives that affects the internai motivation of the animal and its subsequent

behaviors) conveyed by the communication system. In this study, tne vocal

repertoire of the wolf is under investigation. The main focus is on the chorus

howl, a group vocalization that has been historically classified as a type of

howl, but which may indeed contain far more vocal types than simply howling.

To proceed, the ecology, behavior and described vocal types of the wolf must

first be understood.

Wolf Social Orqanization and Behavior

The wolf, the largest of the non-domestic canids, is a highly social

carnivore for which acoustic communication plays an important role. Wolves

usually live in family units called packs, which typically include one mated pair

and offspring from several years' litters. Wolf packs Vary in size, usually

ranging in size from 2 to 10 individuals, although packs as large as 36

individuals have been reported (Rausch, 1967, cited in Mech, 1974). A social

hierarchy exists within the pack with the dominant male and female, or alpha

pair, at the apex.

In forested areas, and elsewhere where wolves are non-migratory,

wolves are territorial; each pack defends an exclusive home range, or

territory. On the tundra, wolves are migratory by necessity because their main

prey, caribou (Rangifer tarandus grantr), are also migratory. In forested areas,

temton'es are variable in size, typically ranging from 125 to 240 Km2 with

some as large as 555 Km2 in northem Minnesota (Mech, 1977a). The actual

size of a territory is reportedly governed mainly by pack size and prey

abundance (Messier, 1985). Individual ranges are relatively stable in ternis of

both size and location over time (Mech. 1977a; Hamngton & Mech. 1979) and

are actively defended from conspecifics (Mech, 1977a; Fritts & Mech, 1981).

There is evidence that there exists an area of overlap between the territories

of neighboring wolf packs and that this area, called a buffer zone. is contested

(Hoskinson & Mech, 1976; Mech, 1977b; Peters & Mech, 1975). Wolves

spend less time at the periphery of their territories than further within the

defended range to avoid potential encounters with neighboring packs. The

buffer zone is the site of most interpack strife (Mech, 1994). Research has

shown (Hoskinson & Mech, 1976; Fuller & Keith, 1981) that these buffer

zones are selectively utilized by lone, dispersing wolves, sympatric species

such as coyotes (Canis latrans) and prey species (example, white-tailed deer,

Odocoileus virginianos). The buffer zone provides a corridor for prey since

they are less likely to encounter resident wolves in this area. The

maintenance and advertisernent of these territories is accomplished through

scent marking, primarily urination (Peters & Mech, 1975) and vocal

communication, primarily howling (Joslin. 1967; Theberge & Falls, 1967;

Harrington & Mech, 1978a, 1978b, 1979, 1983). Social interactions within the

pack and agonistic interactions between packs make 1 important for the woif

to have a sophisticated vocal repertoire, which includes both long-distance

and short-range vocal types.

Wolf Vocalizations

Vocalizations play a large role in the social interactions amongst

wolves and, consequently, they possess a varied vocal repertoire. Wolf

vocalizations have been classified into four basic types: barks, growls,

squeaks (also called whined whimpers) and howls (Fentress, 1967;

Theberge & Falls, 1967; Field, 1978; Klinghammer & Laidlaw, 1979;

Harrington 8 Mech, lW8a), with subdivision into as many as 1 1 different

types (Schassburger, 1987, 1993). The following descriptions f om the bulk of

information available on wolf vocalkation types to date. While there have

been several studies that described the acoustic parameters of wolf

vocalizations, these have primarily focused on two of the four basic vocal

types, the howl (Joslin, 1967; Mech, 1970) and the squeak (Coscia et. al.,

1991 ; Goldman, 1993; Holt & Hamngton, unpubl. data).

(a) Bark

The bark has been descnbed as a short, noisy, explosive sound

(Harrington & Mech, 1978a; Schassburger, 1993), typically less than 1s

(Tembrock, 1963; Schassburger, 1993). It is a vocalization with a low

frequency, between 320 to 904 Hz (Tembrock. 1963) with emphasis near 500

Hz (Harrington & Mech, 1978a). The bark is uttered singly or in sequences.

Behaviorally, the bark is generally considered an agonistic, alerting vocal type

that may serve to attract attention toward the vocalizing animal (Bekoff,

1974). It has been noted that barking wolves are almost always visually

conspicuous (Harrington & Mech, 1 978a). Researchers have noticed that

when they approached dens (Murie, 1944) or homesites (Joslin, 1967) when

pups were present, or when they approached kill-sites, wolves barked (Mech,

1966). These and other sirnilar observations suggests that the bark may

serve as a defense, threat, warning andor alartn call. The bark is also

observed in conjunction with howling. When these two vocalizations are

uttered together, with no temporal separation, the resulting vocalization is

called the bark-howl.

The bark-howl is composed of 1 or a series of barks that become

incorporated into a long, steady howl with slow frequency modulation.

Structurally, the bark-howl is a variable, long duration (2.5 to 4.5 s), low

frequency (21 0 to 400 Hz), composite vocalization made up of between 1 and

6 barks, in series. followed by one howl (Holt & Watson, unpublished data).

Bark-howls are sometimes uttered in sequences. The bark component is a

short (0.02 to 0.05 s), low frequency (fo = 280 Hz) vocalization with a narrow

frequency range (250 to 293 Hz). From the spectrograph, the frequency rises

sharply at onset and either cuives downward or levels out at the end (Holt &

Watson, unpubl. data). The howl component is hamonically structured (1 to 3

harmonics), of long duration (2 to 4 s), and low frequency (fo 306 Hz, range

195-460 Hz) (HoR & Watson, unpubl. data).

The bark-howl has been observed from both wild and captive animals.

Mune (1944) and Mech (1966) observed bark-howling when they closely

approached wolves. Harington and Mech (1 978b) made similar observations

when they closely approached (wlhin 50 m) a pack of wolves with pups. In

captivity, when wolves are approached by unfamiliar persons (Field, 1978),

and when persons approach the den when pups are present (Holt & Watson,

unpubl. data), one or several wolves bark-howl. In the study by Holt &

Watson, it was also obsenred that in 27 of 44 occurrences of bark-howling,

the animal vocalizing was the alpha male who positioned himself in a visually

conspicuous position (the rernaining cases were either started by a

subdominant male, n=5 or an unidentlied animal, n=8). Also, there was a

trend toward a decrease in the number of cases of bark-howling as the pups

got older and spent less time inside the den. These observations would

suggest that the bark-howl is some form of alam, or threat call, perhaps to

draw attention away from the den and vulnerabie pups.

(b) Growl

The growl has been descnbed as a deep, course sound (Hamngton &

Mech, 1978a). Structurally, the growl has a reported frequency range

between 250 and 1500 Hz, with the fundamental around 800 Hz (Tembrock,

1963). Schassburger (1 993) characterized the growl as having a fundamental

frequency in the range of 70 to 2175 Hz. Loudness and spectral fom affect

the range of the growl; Joslin (1967) suggested that the growl is audible at

less than 200 m. The growl is also described as a long duration, continuous

vocalization lasting from cl to several seconds (Field. 1978; Schassburger,

1993). It is thought that the primary contexts in which growling occurs are

waming, defense, threat, attack and dominance (Fentress, 1967; Fox, 1971 ;

Field, 1978; Harrington & Mech, 1978a; Schassburger, 1993). It has been

noted that assertions of dominance, defense of food, and other agonistic

behaviors are often accompanied by growling (Harrington & Mech, 1978a). A

growl from the mother wolf can send pups to the den in times of danger. Field

(1 978) observed that there was a peak in the number of growls during the fall

and during the month of February, while growls were also more numerous

during the late aftemoon and early evening when feeding behavior was more

evident. Also in the study, males growled more often than females. In

general, not much attention has been directed toward research into the growl.

(c) Squeaks

Squeaks, also referred to as whines and whimpers, are short, high

frequency vocalizations which play a role in close social interactions within

the pack. Structurally, the squeak is harmonie, of short duration (0.1 to 0.5 s)

and high frequency (2500 to 5500 Hz), and is often produced in sequences of

varying length (Fentress, 1978; Fentress. Field & Parr, 1978; Field, 1978;

Goldman, 1993; Holt & Harrington, unpubl. data). Squeaks have been shown

to be individually distinct vocalizations for adult wolves. with the fundarnental

frequencies being significantly different between individual wolves (Goldman,

1993; Holt & Harrington, unpubl. data). Behaviorally, the squeak has been

described in several contexts, between pups and adults and between adults.

Pups respond differentially to the squeaks of the mother and to the squeaks

of other adult fernale care-givers, with the mothets squeaks being able to

draw the pups out of the den (Fox, 1971; Goldman, 1993). Wolves exhibit

cooperative pup rearing and it is significant that they recognize the voice of

the mother and other familiar adults. Also, pups can elicit a response from

adults with their squeaks. Fox (1971) noted that when pups are cold, hungry,

or in pain, they squeak to solicit care from the adults. Coscia (1995), however

observed that pups elicit more parental care with screams than squeaks from

birth to 21 days of age, when squeaks first begin to appear in the vocal

repertoire. Pups have also been observed squeaking when the adults retum

to the home-site, perhaps as a greeting (Peterson, 1974; Voight, 1973).

Between adults, the squeak has been observed in close contact interactions.

such as greetings, submissive behavior by subordinate animals, and during

courtship (Harington & Mech, l978a). Following Morton's (1 9T7)

motivational-structural niles, the squeak is considered a Yriendly', non-

aggressive vocalization that is used for short distance communication within

the pack.

(d) Howls

Howls, the most conspicuous of the wolf's vocalizations, have been the

most extensively studied of al1 the wolf vocal types. The wolf howl has been

described as a highly variable, long-distance vocalization. Howls may cany

over distances up to 10 Km (Joslin, 1967; Hankgton & Mech, 1978a).

Stnicturally the howl is classified as a continuous, harmonic vocalization with

a frequency range between 150 and 780 Hz (Theberge & Falls, 1967;

Hanington & Mech, 1978a; Schassburger, 1987, 1993) and up to 12

harmonic overtones (Theberge & Falls, 1967). In a study by Theberge and

Falls (1967), some 700 howls were recorded from three wolves and it was

found that the duration of the howls ranged from 0.5 to 11 s, indicating that

the duration is quite variable. However, howls are generally considered to be

vocalizations of long duration, with 93% of adult howls lasting at least 3 s, and

the majority of those being between 4 and 6 s in duration (Theberge & Falls,

1967; Harrington & Mech, 1978b). Howls are often uttered in sequence,

termed a bout. Joslin (1 967) found that for a wild wolf replying to his howl

imitation, the bout lasted 35 s, with the wolf uttering several howls. Hamngton

and Mech (1978b) found similar results in Minnesota where individual reply

bouts lasted approximately 10 s, with one wolf uttering 35 individual howls

over a span of 3.5 minutes (this howl bout was not elicited by the authors).

Research has also shown that the amount of howling follows daily and

seasonal patterns. In ternis of daily patterns, Hamngton and Mech (1978b)

found that for two packs in Minnesota (Harris Lake and Jackpine packs) the

majority of howling occurred between the hours of 20:OO and 11:00, indicating

that wolves howl predominantly more at night and early moming. Other

authors have found similar trends for captive (Zimen, 1971 ) and wild wolves

(Rutter & Pimlott, 1968). Seasonally, howling increases from the fall into

winter (October to Febniary), and peaks around the breeding season, in

January/ February (Hamngton & Mech, 1978a,b). Similar results were

observed with captive wolves. Klinghammer and Laidlaw (1979) observed

that unaccompanied howls increased (from e5 to between 30 and 40 par

week) during the breeding season.

Howls have been ascribed several functions. It's been argued that

howls function primarily in the advertisement and maintenance of tedories,

as well as in pack cohesion (Joslin, 1967; Theberge & Falls, 1967; Hamngton

& Mech, 1978a,b, 1982; Harrington, 1989). Howls serve to both increase and

decrease the distance between animals and appear to function both within

and between packs. It is thought that howls cany information such as

individual identity (Joslin, 1967; Theberge & Falls, 1967; Rutter & Pimlott,

1968; Voight, 1973; Tooze et. al., 1990), location and the motivational state of

the animal (Hamngton, 1 987).

Wolves howl alone (solo howling) and as part of a group (chorus

howling). Solo howls are thought to serve several functions. One such

function would be that of pack assembly. It was observed that when captive

(Young, 1944) and wild (Murie, 1944; Mech, 1966) wolves were separated

from their pack mates, they howl. Murie (1944) described 5 separate

occasions when an individual wolf howled after having been separated from

its pack mates and was later reunited with the pack as a result. In a similar

fashion, howls may play a role in the formation of new packs (Zimen, 1971).

Two basic classes of solo howls have been described, flat howls and

breaking howls. Flat howls have a relatively unmodulated frequency, whereas

breaking howls are more modulated (Harrington & Mech, 1978a). Flat howls

were found to have a lower mean fundamental frequency and occur when a

wolf closely approaches an intnider, possibly indicating a context of high

aggression. Breaking howls tend to be higher in frequency (Harrington &

Mech, l978a). Morton (1 977), theorized that animal vocalizations follow

motivational-structural rules and that lower frequency vocalizations indicate a

more aggressive context. Tooze (1987) described a third type of solo howl,

called the 'woa-woa' howl, which was characterized by one short howl

followed by between 5 and 13 aborted howls. These were considered rare,

being more frequently heard from single wolves isolated from their pack

mates.

When two or more wolves in a pack howl together, the resulting

vocalization occurs as a chorus. The chorus howl has been described as a

vocalization in which one wolf begins howling, with other pack mernbers

joining in, until several, or all the mernbers of a pack are howling together

(Joslin. 1967). It has been described furlher as a highly contagious event

within the pack (Crisler, 1958), accompanied by tail wagging and face

nuzzling (Harrington & Mech, 1978a). Chorus howls are proposed to play a

significant role in interpack communication, primarily functioning in territory

defense (Joslin, 1967; Theberge & Falls, 1967; Hamngton & Mech, 1978a).

Structurally, chorus howls are highly variable in terrns of frequency

modulation, duration of response, number of individuals in the pack that

participate and the manner in which the animals enter into the chorus

(Theberge & Falls, 1967; Hamngton, 1975; Harrington & Mech, 1982,

Hamington, 1989). Howis that begin the chorus tend to be lower frequency,

longer and less modulated than subsequent howls, which tend to be shorter

duration and more modulated than solo howls (Joslin, 1967; Hamngton &

Mech, 1978; Tooze, 1987). The chorus, while variable in duration, averages

between 60 s (Minnesota: Harrington & Mech, 1978a) and 85 s (Ontario:

Joslin, 1967). The chorus may provide information on pack identity, location,

motivation and potentially pack size (Mech, 1970), although the latter has

been questioned (Harrington, 1989). Two forms of the chorus howl have also

been proposed: hamonious and discordant (Schassburger, 1993). It has

been suggested that elicited choruses are more discordant than spontaneous

ones (no apparent stimulus) (Schassburger, 1993; for rad wolves (Canis

rufus), McCarley, 1 975).

Rational of Present Study

The chorus howl has historically been treated as one form of howl

vocalization (Murie, 1944; Joslin, 1966; Theberge & Falls, 1967; Harrington &

Mach, 1978a, b; Schassburger, 1987, 1993; Tooze, 1987). While much is

known about the wolf howl structurally and of the behaviors associated with it,

the chorus howl has not been deconstructed to observe the extent to which

the chorus incorporates the various vocal types descnbed for the wolf.

Reference has been made to vocal types other than the howl being heard

during the chorus. Tooze (1987) observed that wolves bark frequently during

choruses and that these barks, while isolated from the howls, are often

interspersed with squeaks. Joslin (1 967) observed that in some instances,

barks teminate howling sessions and bark-howling can be heard

interspersed with howls when humans approach closely (Mech, 1966; Murie,

1944; Joslin, 1967; Harrington & Mech, 1978b). Reference has also been

made to squeaks occurring during chorus howls. Harrington and Mech

(1 978a) observed that young and subordinate animals squeak while

attempting to lick the face of other wolves during a chorus howl. Pehaps one

of the reasons why the chorus howl has been described as a f o n of howl is

because of the distances from which choruses are generally heard and

recorded. At distances z 1 Km the predominant vocalization heard and

recorded is the howl. Vocalizations like squeaks and growls would not be

heard at these distances and it is only when choruses are observed and

recorded at close range (within 4 Km) that these associated vocal types can

be more closely analyzed. The purpose of this study then, was to perform a

structural analysis of the chorus howl to identify the component vocal types

associated with the group vocalization.

METHODS

General Description

This study employed playback to elicit chorus howl responses from

captive wolf packs. The elicited responses were then recorded on both video

and audio cassette tapes. The video taping was conducted within 5 to 10 m of

the wolves, while they were vocalizing, giving good recording quality and

ensuring that any vocal types considered short range calls would be recorded

with the def inition required for spectrographic analysis. Du ring spectrographic

analysis, the elicited chorus howl responses were deconstructed to determine

the nature of the variability of vocal types contained within the chorus.

General behaviors associated with these responses were also recorded and

described.

Studv Sites/ Subiects

The study included data from three captive packs of wolves, housed at

three different facilities across the United States. These were 1) Wolf Park,

Indiana, 2) the International Wolf Center, Minnesota, and 3) the Wolf

Education and Research Center, Idaho. The study sites were chosen

primarily on the basis of the facility layout. Each of the three facilities housed

either a single wolf pack, or the wolves were housed such that it was certain

which anirnals were responding to the stimuli. All facilities provided

information about pack structure, feeding schedules and routine handling

procedures. The playback experiments were conducted between August and

December 1995.

During the course of this study, several other facilities were

considered, al1 of which were rejected upon visitation because of their layout.

These included the Wild Canid Survival and Research Center (Missouri),

Carlos Avery Game Farm (Minnesota), Bear Country U.S.A (South Dakota)

and the Metro Toronto Zoo (Ontario). The playback experirnent was also

atternpted with wild radio-collared wolves in Superior National Forest,

Minnesota (U. S. Geological Survey, Biological Resources Division project)

where problems with budget constraints and adverse weather conditions

prevented the collection of useful data.

(a) Wolf Park

Wolf Park, located near the town of Battle Ground, Indiana, is a

privately owned, publicly funded facility. Wolf Park is open to the public for

wolf education and provides students with the opportunity to complete

intemships and practicums in the areas of ethology and animal handling. At

the time of the study, the facility maintained a pack of 8 related (alpha pair

and sibling, as well as several generations of offsprhg) socialized wolves as

well as several other wolves housed singly or in pairs some distance from the

large pack. Also housed at Wolf Park were 2 coyotes (Canis latrans), 1 Red

fox ( Vulpes vulpes) and a herd of 22 North Amencan bison (Bison bison).

The 8 wolves in the main pack (Table 1) were the study animals.

Prelirninary observation showed that the presence of the singly housed and

paired wolves did not intetfere with the study pack's responses to stimuli, or

with subsequent recording. The pack was maintained in a semi-natural,

sparseiy treed (mostly deciduous), 2.6 ha enclosure which encompassed a

smôll lake to which the wolves had access. There were several wooden den

boxes in the enclosure. The wolves were fed once weekly a diet of road-kilied

deer (Odocoiieus virginianus) and the carcasses of domestic Iivestock

donated from fams in the vicinity. The wolves were socialized to humans and

received close physical contact with several people on a weekly basis. The

playback experiment was conducted between August 4 and August 25,1995.

(b) lntemational Wolf Center

The lntemational Wolf Center, located in the town of Ely, Minnesota, is

a not-for-profit organization. The center is open to the public as an

information/ leaming facility, and to students for intemships. At the time of the

study the IWC rnaintained a pack of 4 related (siblings), socialized wolves

(Table 2) housed in a forested, semi-natural 0.5 ha enclosure, which included

automatic water dispensers and a den box. Twice weekly, the animals were

fed a diet of road-killed deer, prepared high protein dog kibble, and various

assorted fresh meats. The wolves were socialized to humans and received

close physical contact with several people on a daily basis. The playback

experiment was conducted between September 15 and October 31,1995.

(c) Wolf Education and Research Center

The Wolf Education and Research Center is located at the base of the

Sawtooth Mountains, in Stanley, Idaho. The center was open primarily to

students and volunteers at the time of the study. A pack of 6 (related siblings

and non related individuals) socialized wolves (Table 3) was maintained in a

heavily forested, semi-natural 6.9 ha enclosure which contained several den

boxes, and water dispensers. The animals were fed a weekly diet of road-

killed deer and other assorted rneats, as well as prepared dog kibble. The

wolves were socialized to people however, they received minimal close

physical contact. The playback experiment was conducted between

November 18 and December 1,1995.

Table 1. The structure of the study pack at Wolf Park, August 1995.

MALE 7 ALPHA

FEMALE 7 ALPHA

MALE 2 SUBDOMINANT

SUBDOMINANT

Table 1.

Table 2. The structure of the study pack at the International Wolf Center,

October 1 995.

EËE AGE (YEARS) SOCIAL STATUS 1

MALE 2 ALPHA

FEMALE 2 ALPHA

FEMALE 2 OMEGA

Table 2.

Table 3. The structure of the study pack at the Wolf Education and Research

Center, December 1995.

FEMALE

4 ALPHA

3 ALPHA

4 SUBDOMINANT

3 SUBDOMINANT

3 SUBDOMINANT

3 SUBDOMINANT

Table 3.

Stimulus Creation

The stimuli for the playback experiment were created primarily to elicit

chorus howl responses from the captive packs involved in this study. They

were also created to detemine whether the number of wolves howling, the

fundamental frequency and the coefficient of frequency modulation of the

stimulus influenced the structure of the responses, in particular, whether

wolves in any way mimicked the parameters of the stimulus. For example, do

wolves modulate their choruses more in response to more modulated stimuli?

Many animals mimic the vocalizations of conspecifics, other species and even

background noises (Zahavi & Zahavi, 1997).

The stimuli for the playback experiment were artificially created from

recorded human imitations of wolf howls. Artificially created stimuli are now

recognized as having many advantages over natural signals for playback

experiments, particularly because they avoid a number of design problems

arising from the multidimensional nature of natural signais (Gerhardt, 1992).

Advantages include: 1) the quality of the stimuli can be kept constant, 2) the

total duration of the stimuli can be set to ensure a level of sensory input

appropriate for the study species (Pepperberg, l99Z), and 3) the identlies of

participants in creating the stimuli can be tailored for the particular experiment

(McComb, 1992).

Human howl imitations were chosen because they can be produced

with relative ease, and can be manipulated to great extent. Human howls are

also effective at eliciting responses from woives (Pimlott, 1960). Such howls

have been used as stimuli to study many aspects of wolf vocal behavior:

general characteristics of the howl (Joslin, 1967; Theberge & Falls, 1967;

Harrington, 1975), aggression (Hamngton, 1987), the effects of howling on

territory maintenance (Hamngton 8 Mech, 1979, 1983), estimation of pack

size (Theberge & Strickland, 1978) and to census wolf packs (Hamngton &

Mech, 1982; Fuller & Sampson, 1988).

The human howl imitations were recorded at Wotf Park with the

cooperation of the facility director and four employeed volunteers. Al! stimuli

participants had previously demonstrated skill at eliciting responses from

wolves with their howl imitations. The human howls were recorded on two

separate days (one day recordings would have been preferred however the

human howlers had conflicting schedules making this unfeasible), and factors

such as environmental conditions (wind velocity and temperature), distance

(10m) and recording volume were kept constant to ensure consistent

recording quality. The stimulus howls were recorded on Sony UCX-S9O audio

cassette tapes, using a Sony Professional Walkman (WM-DG) and a tripod

mounted Sennheiser Super Cardioid shotgun microphone fitted with a

Sennheiser MZW 415 windscreen. The voltage required to power the set-up

was obtained by attaching both the Walkman and the microphone to a

NagralKudelski amplifier/rnonitor which was, in tum, attached to a 12 Volt

vehicle battery.

One male individual produced two howls. one (Howl 1) was

unmodulated (CoFM=1.2%) and was labeled as Stimulus 1, and the other

howl (Howl 2) had a higher level of modulation (CoFM=2.6%) and became

Stimulus 2. Four individual howls (CoFM<G%) were recorded, one from each

of the four remaining participants. These howls (Howls 3-6) were used to

produce Stimulus 3 and Stimulus 5. Stimulus 4 (2 wolves) and Stimulus 6 (5

wolves) were recorded as ' natural ' choruses. In both cases the individual

that produced Howl 1 and Howl 2 began the chorus. A second individual

(producer of Howl 3) joined in the chorus to produce Stimulus 4, whereas for

Stimulus 6, four individuals (producers of Howls 3-6) joined the chorus in

succession. varying their howls over the course of the chorus.

The finalized stimuli were produced using the Sound orge^^ 2.0

(Sonic Foundry, 1994) computer software package. Stimulus 1 and Stimulus

2, representing one wolf howling, were synthesized as follows: previousw

recorded Howl 1 and Howl2 were saved individually as 16 bit wave form files.

Each howl was copied 5 times and a sequence of 6 identical howls,

separated by 1s intervals, was synthesized for each howl. The sequence

synthesized from Howl 1 became Stimulus 1, with a total duration of 36 s and

the sequence synthesized from Howl 2 became stimulus 2, with a total

duration of 41 S. Stimulus 3, representing 2 wolves howling, was synthesized

by taking the howl sequence recorded from Howl 1 and overlapping it with a

sequence synthesized in the same way, using Howl3. The overfap was offset

so that the Howl3 sequence started 3 s after the onset of Howl 1 sequence.

The total duration of Stimulus 3 was 42 S. Stimulus 5, representing 5 wolves

howling, was synthesized using the same procedure as that for Stimulus 3.

Howl 1 sequence, Howl 3 sequence. and three additional howl sequences

from three different individuals were overlapped in a staggered manner to

give a final chorus (Stimulus 5) with a duration of 51 S. Stimulus 4 (2 wolves)

and Stimulus 6 (5 wolves) were recorded as ' natural ' choruses. Neither was

modified. Stimulus 4 had an overall duration of 45 s and Stimulus 6 had

duration of 46 S. The six resulting stimuli (Table 4) were recorded from Sound

ForgeTM, through a Sound BlasterTM card ont0 Sony UCX-S9O audio

cassettes.

Table 4. Description of the stimuli used for the playback experiment.

Table 4.

Plavback Experiment Procedures

The stimuli were broadcast to the packs using a Sony Professional

Walkman, through a Nagrd Kudelski (DMS) arnpllier (frequency response

20-20000Hz) set on extemal output to accommodate a 2OWatt Alpine car

audio speaker. Peak sound pressure levels were kept constant at 100dB, at

lm from source. The speaker was poslioned 0.75m from the ground and

tilted at a 45" angle to sirnulate the approximate height and position of a wolf

howling. It has been observed that even slight differences in the position of

the speaker during broadcast of a signal can resuit in substantial changes in

the level of sound received by the subjects (Wiley & Richards, 1978). The

broadcast signal was directed toward the pack's enclosure frorn a distance of

300m from the periphery. This distance allowed for a more natural sound

being received by the pack, as increasing the heterogeneity of the

environment would induce echoes and cause attenuation of the signal

characteristic of the natural situation. Observations prior to the individual

playback experiments confirmed that the stimuli could be heard throughout

the entire area of each enclosure. Also, Harrington and Mech (1983) found no

evidence that a wolf pack's probability of reply, in response to a stimulus,

depends on the pack's location within its temtory. Because of this, the

position of the pack within their enclosure was not taken into account at the

onset of stimulus broadcast.

Responses were recorded on both audio cassettes (Sony UCX-SSO)

and on video cassette, w%h video equipment provided by the individual

facilities. Both the video recording equipment and video cassettes used were

different for each pack. For each response, the video recording equipment

was positioned within 5m of the enclosure perimeter. The exact location was

chosen for its unobstructed view of the area within the enclosure in which the

wolves spent the rnost tirne (these data were obtained by persona1

observation and information provided by the facility staff). The video camera

was positioned at the same location for each session, regardless of where the

wolves were within the enclosure at the beginning of the broadcast session.

Wolf Park and the International Woif Center provided a volunteer to operate

the video camera. At the Wolf Education and Research Center, the video

camera was tripod mounted.

The playback experiment followed a set protocol. Each pack received

a total of six different stimuli over the course of six separate playback

sessions. Each playback session went as follows: It began with an initial 10

minute observation period, during which the location of the wolves within the

enclosure, their behavior, and environmental conditions were noted. A

playback period followed with the broadcast of a pre-selected stimulus

(chosen by random nurnber generator). If a vocal response was elicited, the

wolves were observed for 10 minutes after the conclusion of the response .

and the session was ended. If no vocal response was elicited an alternative

procedure was followed. Rather than having a 10 minute obseivation period.

then ending the session, a 20 minute observation pet-iod was followed by the

rebroadcast of the stimulus. If a vocal response was elicited a 10 minute

observation period followed and the session ended. This procedure was

repeated one more time if a vocal response was not elicited by the

rebroadcast. Each playback session was separated by at least 48 hours to

avoid habituation.

The playback sessions were conducted between 1 hour before sunset

and 1 hour after sunrise. Wolves are most active during these periods

(Harrington & Mech, 1979; 1982) and at these times environmental conditions

are more stable. Wind is reduced and temperature inversions near the

ground, which can have an affect on attenuation, are less common (Wiley &

Richards. 1 978).

Data Analvsis-Acoustic

The data obtained from the playback experiment were taken directly

from the video cassettes. The audio cassettes provided acoustic back-up.

The video cassettes were viewed on a Panasonic video monitor. The acoustic

component of the video was digitized using the SignalTM (Engineering Design,

1990) sound analysis systern, which includes the Real Time SpectrographTM

(RTSTM), designed speclically for the spectral analysis of animal

vocalizations. RTSTM perrnits on-screen viewing and measurement of each

sound sample. The analogue signal undergoes a 512 point Fourier

transformation, producing a digitized signal, which is displayed on-screen in

the form of a frequency-time plot (spectrograph). For each vocal response, a

spectrograph scrolled across the screen in real time. This spectrograph could

be Yrozen' to record the specific frequency (Hz) and time (s) measurements

using crosshair curson.

The acoustic data measured from the spectrographic analysis of

responses from the playback experiments were:

1. Total duration of response (s), measured as the duration between the - initial vocalization after the onset of the stimulus broadcast and the last

vocalization that was followed by a 5s interval in which there were no

vocalizations. The time to reply was also measured as the time from the

stimulus broadcast onset to the beginning of the response.

2. Total number of individual vocalizations of each of the 5 identified types: -

howls. barks, bark-howls, growls and squeaks. These vocal types were

identified both by ear (al1 have characteristic sounds) and by

spectrographic (Figure 1) cornparison between each vocalization in the

response and a set of standard vocal types based on previous research

into acoustic parameters (Table 5).

3. The mean fundamental frequency (fo) of al1 vocalizations within the - response. The fo (Hz) was sampled at 0.1 s intervals for the duration of

each vocalization; these were combined to give an overall mean

frequency of the whole response.

4. Durations of al1 vocalizations within the response (s), which were divided - into vocal types and averaged to give a mean duration of vocalizations in

the response.

5. The coefficient of frequency modulation (CoFM) was calculated for al1 - vocalizations with a duration >Is. The CoFM measures the rate of

frequency modulation relative to the mean fundamental frequency of the

individual vocalization (Appendix 1 for CoFM equation).

The 17 chonises analyzed were considered together because they

constitute one category of wolf vocalizations regardless of how they were

elicited. The percent occurrence of each vocal type (howl, bark, bark-howl,

squeak and growl) was measured for each chorus, then the mean was taken

of the vocal types to give a general description of the chonises.

The vocal types within the choruses were analyzed separately to

determine their structural characteristics. Values for mean duration and

frequency, and the CoF M (for vocalizations >1 s in duration) were calculated

for each vocal type. This permitted cornparison with previously established

values for these vocal types.

The stimuli in the study were designed to elicit chorus responses

from the packs as well as to make preliminary observations into the possibility

of vocal rnimicking in wolves. To make these observations, the chonises

elicited from each pack, were pooled by stimulus (example: Stimulus 3, n=3)

and analyzed for total duration and CoFM. These values were then plotted

against values from the stimuli.

Data Analvsis- Behavioral

The following behavioral information was obtained from the video

record of each response.

1. The animal which began the response (if visible).

2. The total nurnber of animals that paiticipated in the response (if visible).

3. The position of the wolves in relation to each other dui-ing the response,

and their associated postures and behaviors. For example, were the

animals laying down, standing. tails wagging, face nunling, etc.

Fiaure 1 . Spectrographie representation (stylized) of characteristic forms of

the A) bark, B) growl, C) squeak, D) howl and E) bark-howl vocal types.

Figure 1.

Table 5. Structural characteristics of the bark, growl, squeak. howl and bark-

howl vocal types (from Tembrock, 1967; Schassburger, 1993 and Holt &

Watson, unpubl. data.).

HOWL

TYPE NOISY- HARMONIC CONTINUOUS SPECTRUM

BARK

GROWL

SQUEAK

Table 5.

CAL (HZ) 145-2720

250- 1500

2500- 5500

BARK-HOW L

c 1

< 1- SEVERAL

2 1 0-400 2.5- 4.5 NOISY- HARMONIC

0.1 - 0.5 -

HARMONIC

RESULTS

Composition of the Chorus Howl

The data show that the group vocalization referred to as the chorus

howl is actually comprised of a variety of vocal types in addition to howling

and should be categorized sirnply as a 'chorus" rather than as a fom of howl.

Figure 2 dernonstrates the variety of vocal types contained within a chorus. In

al1 choruses analyzed (n=17), at least two vocal types were always present:

howls and squeaks. Howls comprised the largest number of vocalizations

(calculated as [the number of sounds of one vocal type + the total number of

vocalizations] x 100%) within the chorus (meanSb%t 14%), followed by

squeaks (mean=36%1 I l%) , barks (mean=7O& 8%), growls (mean=O.6%1

1.2%). bark howls (mean=û.O4%t 0.1 1 %) and rniscellaneous vocalizations

that could not be categorized (mean=O.3%1 0.6%). Using total duration of

each vocal type to show the composition of choruses, it was found that howls

represent 75.6 % of the durations of the choruses, followed by squeaks at 23

%. barks at 1.2 % and growls at 0.3 %.

In at least one chorus from each pack, the howl was not the most

numerous vocal type. For the Wolf Park pack, two of five recorded choruses

had a higher percentage of squeaks than howls (Figure 3). Barks were only

heard during one chorus. In this case, however, the barks made up 21% of

the vocalizations.

Fiaure 2. Spectrographs of the beginning, mid section and end cf a chorus

vocalization. showing the variability of vocal types contained within.

2A) Chorus beginning

2B) Mid chorus

2C) End of chonis

- 0 1 2 3 4 s

mu3 (SI

Figure 2A.

mm0 (SI

Figure 28.

Figure 2C.

Fisure 3. The vocal type composition (%, based on the number of each

vocalization) of each chorus recorded at Woff Park (August, 1995). For

Stimulus 1 and 2, no vocal response was elicited. indicates a spontaneous

chorus. This chorus, for which there was no apparent stimulus, was recorded

during obseivation (before stimulation). The table below gives the number of

each vocal type in the choruses.

Howl squeak bark Bark growl misc. Total

howl

This chorus also contained growls (3 growls out of a total of 220 individual

vocalizations); growls were heard in only one other chorus. No bark howls

were uttered in any of the choruses.

For the International Wolf Center pack, the chomses were al1 (n=6)

dominated by howls (Figure 4). All choruses contained from 48 to 64 % howls

with a variable percentage of squeaks (20-45%). Five of the choruses also

contained barks, two contained growls, and one bark howl were heard. As for

the Wolf Park NP) pack, the growls were heard in choruses that also

contained barks, and in one of these, a bark howl. The Wolf Education and

Research Center (WERC) pack (Figure 5) showed a pattern of vocal types

similar to that at both the International Wolf Center (IWC) and Wotf Park.

Similar to WP, two of the six choruses contained a higher percentage of

squeaks than howls. However, in terms of the number of choruses that

contained b a h , the WERC pack showed more similarity to the IWC pack.

Barks occurred in varying amounts (3 to 19%) in four of the six choruses and

growls (range 1 to 4%) were heard in al1 chonises that contained b a h . One

of these choruses (both growls and barks present) also contained the only

other bark howl heard during the study. As with WP, a natural chorus (no

apparent stimulus) was recorded at WERC. which consisted entirely of howls

and squeaks.

Fiaure 4. The vocal type composition (%, based on the number of

vocalizations) of each chorus recorded at the International Woif Center (Sept./

Oct. 1995). The table gives the number of each vocal type for each chorus.

Howl squeak bark bark growl Misc. Total

howl

21 15 4 O 1 O 41

1 08 37 38 O O O 183

93 81 7 O O 3 1 84

1 34 97 39 1 3 3 277

81 43 3 O O O 127

1 09 89 O O O O 198

Fiqure 5. The vocal type composition (%, based on the number of

vocalizations) of each chorus recorded at the Woff Education and Research

Center (November 1995). No vocal response was elicited by Stimulus 1. '

indicates a spontaneous chorus. This chorus, for which there was no

apparent stimulus, was recorded during observation.

Stim. How! squeak bark bark- growl misc. total

howl

Properties of Chorus Vocal Tvpes

The vocal types contained within the chorus vocalizations were

analyzed individually and corn pared to previously reported structural

properties. Frequency and duration were the main properties examined. For

howls, CoFM was calculated.

(a) Howls

The howl was the major vocal type obsenred in wolf choruses. Three

forms of howls were descnbed from the data; one fom closely resembled

the solo howl, a second form the breaking-howl, and a third fom

resembled the 'woa-woa' howl described by Tooze (1987). The solo howl

accounted for 96% of al1 recorded howls. One breaking-howl and a total of

62 'woa-woa' howls completed the total (n=1702).

The solo howls (n=1639) in the study had a rnean fF 512 I 231 Hz, a

mean duration of 1.78 i 1 .O2 s, and the CoFM averaged 3.2%. The one

obseived breaking-howl had a fF 486 t 103 Hz, a duration of 1.24 s and

a CoFM = 6.1%. Tooze (1987) described the 'woa-woa' howl as a howl

that begins with a short howl which is followed by between 5 and 13 very

shor? 'aborted' howls. The woa-woa howl in Tooze's (1987) study was

heard from an animal that had recently been isolated from its pack mates.

The present study identified potential woa-woa howls in the chorus. The

'woa-woa' howls observed in choruses (n= 62) had a mean f s 504 r 21 5

Hz, a mean duration of 1.45 I 0.8 s and a calculated CoFM = 8.1 %. These

'woa-woa' howls were described as between 5 and 9 very short (<0.6s),

chevron shaped howls, separated from each other by time intervals so

short in duration that each syllable appeared joined. These howls occuned

in al1 but 2 choruses and tended to occur in the middle of the chorus.

Figure 6 shows spectrographie differences between a characteristic solo

howl, breaking-howl and woa-woa howl from this study. It was also

observed that when wolves woa-woa howl they keep their heads in the

characteristic up-tilted position and the sound is produced by sequentially

opening and closing the mouth (Figure 7).

(b) Squeaks

The squeak vocal type was the second most abundant vocalization

observed in the choruses. The squeaks analyzed for this study (n= 1202)

had a fa= 2465 I 1123 Hz and a mean duration of 0.76 i .23 S. Squeaks

were uttered singly or in trains of between 2 and 5. Observations showed

that the squeak is heard over relatively short distances. At 3-5 m distance,

squeaks were readily heard by obseivers, whereas at distances of 300 m

or greater, they were difficult to hear (squeaks were barely discemable

from the stimulus broadcast area, positioned at 300 rn from the outer

perimeter of the wolf enclosure). Figure 8 shows squeaks characteristic of

those recorded in the study.

Fiqure 6. Spectrograph comparing a solo howl, a breaking howl and a woa-

woa howl.

A) solo howl

B) breaking howl

C) woa-woa howl

Figure 6.

Fiaure 7. Sequence of photographs shoMng the position of the head and

mouth of a wolf utîering a woa-woa howl. The wolf in question is a

subdominant male at the Wolf Education and Research Center.

Figure 7.

Fiaure 8. Spectrograph of squeaks contained within a chorus. In this

spectrograph the squeaks appear in a train of 4 individual squeaks, at a

frequency of 2500Hz.

Figure 8.

(c) Barks, Bark-howls and Growls.

Barks were observed in 10 of the 17 choruses recorded. No barks

were uttered in either of the 2 spontaneous choruses. Barks (n= 284) were

short duration (mean = 0.17 t 0.07 s), with a mean fos 340 I 51 Hz. Barks

were uttered singly or in trains from between 2 and 17 individual barks.

Figure 9A shows barks from one animal that were uttered in a train of 12

barks, followed by a train of 3. followed by a single bark uttered during a

chorus.

Two bark-howls were observed in the study, they consisted of 3 4

barks followed by one long howl (Figure 9B). One bark howl was uttered in

the middle of a chorus that contained a large percentage of barks (13%),

as well as 4 growls. The second bark howl was observed under the same

conditions (chorus with barks and growls).

Growls were observed in 8 of the 17 choruses recorded. No growls

were uttered in the spontaneous choruses. Of the growls (n= 11) analyzed

for this study it was found that growls had a variable duration (from 0.46 to

1.55 s, mean 0.93 s) and a low frequency ( f p 237 t 18 Hz) with a broad

spectrum. Figure 9C shows a growl characteristic of those seen in the

study. It is of importance to note also that growls were heard along with

squeaks, during episodes of tail-wagging, face nuuling behaviors.

Schassburger (1993) stated that growls occur solely in aggressive

contexts and that squeaks occur solely in non aggressive contexts, yet

here they occur together.

The vocal types observed in the chorus howls were cornpared to the

accepted standards for those vocal types. Table 6 shows values for frequency

and duration for the howl, squeak, bark, and growl from previous reports and

from this study. Ail the values found for frequency and duration of the vocal

types contained within the choruses fall within the prescribed ranges (Table

6). In this study, barks were described as having a mean fF 340 t 51 Hz.

This corresponds to the frequency found by Tembrock (1 963) which ranged

from 320 to 904 Hz.

Fiaure 9. A) Spectrograph of a train of barks contained within a chorus.

B) Spectrograph of a bark-howi uttered during a chorus.

C) Spectrograph of a growl uttered during a chorus.

Sounds at 2500 Hz are crickets.

Tim (SI Figure 9 A.

Figure 9B.

T h e (SI

Figure 9C.

Table 6. Cornparison of the published values for frequency and duration for

the howl, squeak, bark and growl, to the corresponding values observed in

this study. For the howl, a = solo, b = breaking-howl, c = woa-woa howl.

l Schassburger (1 993)

* Tembrock (1 963)

HOWL 1 50-780 a, 281 -743 0.5-1 1.5 a. 0.76-2.80 b. 383-589 b. 1.24 C. 289-71 9 C. 0.65-2.25

BARK 1 45-1 70' 287-39 1 O. 10-0.24 320-9042

GROWL 250-1 500 21 9-255 cl -several 0.43-1.43

Table 6.

Structural Characte ristics of Choruses

Data were collected on the duration of the choruses, the time required

for packs to reply to stimuli, the overall frequency of the choruses, and

modulation. Choruses had a variable duration, ranging from 45 to 210 s, wlh

a mean of 101.5 44.4 S. This mean duration is longer than averages found

by Joslin (1967) (85 s for free-ranging packs in Ontario) and Hamngton &

Mech (1978b) (60 s for free-ranging packs in Minnesota). The time to reply

was highly variable; packs began to reply an average of 36.5 * 29.4 s (n=15)

after the onset of the stimulus broadcast. This mean is 0.5s longer than the

shortest of the stimulus. Ten of the 15 choruses elicited by a stimulus began

before the stimulus had ended. The remaining choruses began after the

stimulus ended. This is consistent with findings by Hamngton (1989), who

found that wolves often begin howling before the stimulus is terminated. The

wolves in the latter study were free-ranging and the stimuli were human howls

uttered in situ.

The overall mean frequency of vocalizations in each chorus was also

variable, ranging between 506.1 and 1415.9 Hz, with a mean of 881.9 t 250.1

Hz. Because the mean frequency of a chorus took into account al1

vocalizations uttered, the relatively high frequency range reflects the inclusion

of the many high-pitched squeak vocalizations that were present in most

choruses. The CoFM, calculated as a mean for al1 choruses, indicated a

modulation rate of 5.9 I 2.5%/ second. This number is low due to the

exclusion of squeaks, growls and barks in the calculation because these

vocalizations were generally less than 1s in duration. Thus CoFM was

calculated solely on howls greater than 1 s in duration.

Effect of Stimuli on Choruses

The stimuli were designed not only to elicit chorus responses from the

wolf packs but also to observe whether or not wolf packs mimic the stimulus

they reply to. The stimuli increase in duration and CoFM from Stimulus 1 to

Stimulus 6. If wolves mimic the stimulus, a trend should have been observed

in both duration and CoFM. The data for duration exhibit a slight trend.

However, duration was the longest (mean = 136 + 34.8 s; n=3) in response to

Stimulus 4, shortest in response to Stimulus 1 (47.8 s, n=l), shorter than the

duration of the spontaneous chorus (mean = 95.7 I 28.7 s; n=2). The data for

CoFM showed a very slight trend toward higher CoFM of the chorus as the

CoFM of the stimulus increased (Figure 10). In the case of CoFM, the less

modulated choruses were the spontaneous choruses (CoFM = 1.8%) and the

most modulated were those in response to Stimulus 5 (CoFM = 6.7%). The

CoFMs for the remaining responses fell between those for Stimulus 5 and the

spontaneous choruses. These trends rnay indicate mimicking, however the

sample size for each stimulus may not give means that accurately represent

the trend. 1

Fiaure 10. Duration and CoFM for chorus responses to each stimulus.

Behavioral Characte ristics of Choruses

Where the identity of the animal who began the chorus was known, six

were started by the alpha male and two were started by a subdominant male.

At Wolf Park and the Wolf Education and Research Center, wolves often

stood on structures within their enclosure to vocalize. These structures were

either artificial, like den boxes, or natural such as fallen trees. This was not

observed at the International Wolf Center. even though there were such

structures in the enclosure. These wolves did, however, stand in a section of

the enclosure that was higher in elevation than the area in which they spent

their time during observation periods. Also, wolves were in a standing poslion

when vocalizing during choruses, except in one case. At Wolf Park, the alpha

male started a spontaneous chorus while lying down. As other wolves joined

the chorus it continued to remain lying down throughout the chorus. Figure 11

shows the alpha male (lying down, foreground) and a subdominant male

vocalizing during the chorus.

Data were collected on the number of pack members that participated

in the choruses. It was observed that at Wolf Park, the omega animal (lowest

ranking animal), an adult female wolf, never participated in the choruses with

the other wolves. This wolf was mobbed repeatedly by the other pack

members when she was in close contact with them and was therefore seldom

seen in their vicinity (persona1 communication from P. Goodman). Also at

Wolf Park, not al1 pack members participated in the one observed

spontaneous chorus. Only four of the seven wolves participated. the alpha

male, alpha female and two subdominant males. For the packs at the

International Woff Center, al1 wolves participated in al1 the choruses. At the

Wolf Education and Research Center, the wolves were not visible dunng two

of the choruses so it was not possible to detemine if al1 animals participated.

However, in the remaining four choruses al1 wolves participated.

Choruses were characterized by much social interaction arnong pack

mernbers. Face nuuling and tail wagging were observed in al1 choruses. The

animals also stood close together during the chorus. within two to three body

lengths. It was also observed that the wolves, upon hearing the onset of the

stimulus, stood, ears erect, tail down and stared in the direction of the

stimulus broadcast. This behaviour was repeated at the end of the chorus

response and in seven of the 17 choruses, this was seen during a pause

(>ls) near the end of the choruses. In those choruses which had a pause

greater than one second, the wolves abruptly stopped vocalizing, stared in

the direction of stimulus broadcast, and then resumed vocalizing. This would

indicate that the wolves remained aware of the direction in which the stimulus

was broadcast and that they were still attending to it. The wolves during the

choruses remained in close contact with each other.

Figure 11. Photograph showing the alpha male and a subdominant male

during a spontaneous chorus. The alpha male remains lying down while

howling.

Figure 11.

DISCUSSION

Summaw of Maior Findinas

The choruses of wolves contain howls, squeaks, barks, bark-howls and

growls. These vocal types occur in varying amounts with howls being the

most numerous. Choruses also contained a high percentage of squeaks and

barks. The choruses that contained barks were often accompanied by growls

and in two cases, bark-howls. Spontaneous choruses, those not elicited by

any detected stimulus, were composed of howls and squeaks only. When the

vocal types contained within the choruses were analyzed separately, they

corresponded to previous descriptions made for those particular

vocalizations. Three foms of howls were identified, the solo howl, the

breakinghowl and the seldom described woa-woa howl. The woa-woa howl

contributed to the variability of frequency modulation within the choruses. 'The

description of squeaks as short distance vocalizations was further elucidated.

Squeaks that occurred during choruses were heard at distances of between

10 and 20 rn but were not heard at a distance of 300m. This was found by

watching the video and listening to audio cassettes of the responses

concurrently. This confirms their use for close contact communication.

The packs in this study responded vocally at a higher rate to stimuli

containing more than one animal which suggests that choruses are more

effective at eliciting choruses from packs than are the howls of lone animals.

The data were also mildly suggestive of vocal mimicking, or more specifically,

vocal matching in terms of overall chorus length and frequency modulation.

Behaviorally, pack members rallying around each other characterized

choruses. Face nuuling, tail wagging and other close contact behaviors such

as submissive displays were common. Typically, wolves stood to howl, with

head tilted back, ean erect and tails dom. The one exception was a

spontaneous chorus started by the alpha male who was lying down at the

beginning and rernained lying throughout the chorus. The vocalization known

as the chorus howl is composed of several vocal types and while the howl is

the defining feature of the chorus, it should be reclassified as a "chorusn

rather than being referred to as a type of howl as it has been described here-

to-f O re .

Choruses, Structure and Behavior

Choruses were found to be variable in overall duration, vocal

composition and frequency modulation. The choruses contained varying

combinations of howls, squeaks, barks, bark-howls and growls. Howls were

the most numerous vocalizations, followed by squeaks, barks, growls and

bark-howls. This combination of vocalizations may be important in the overall

message contained within the chorus. The inclusion of several vocal types

may seive to alter the motivational states of the animafs in the pack and

thereby alter the chonis. This, in tum, rnay affect the message received by

neighboring packs. For example, a chorus that contains growls and barks

rnay be more aggressive in context that one that contains only howls and

squeaks.

Choruses were variable in overall duration, ranging from 45 to 210 S.

The longest choruses were those with the most vocalizations (range from 27

to 382 vocalizations). Most chonis responses were also started before the

stimulus had ended. This indicated that wolves rnay not attend to the overall

duration of a stimulus choms; rather they rnay listen for the motivational state

of the stimulus pack. The pack rnay be angered, excited, scared, al1

motivations which rnay be transmitted by the choms.

The chonises were variable in terrns of frequency modulation, however

the mean was lower than expected (5.9 r 2.5%). The mean was expected to

be higher because of the highly modulated nature of the choruses. The

modulation of the choruses was calculated as the CoFM of al1 vocalizations

greater than 1s in duration. This calculation however did not give a true

measure of the chorus modulation because squeaks and barks, which can

comprise up to 50% of a chorus and are generally less than 1s in duration,

were not represented in this calculation. In future calculations of the

frequency modulation of chonises al1 vocalizations, both greater than and less

than 1 s in duration, should be included to get a more accurate CoFM which

rnay aid in better defining differences in choruses. This is especially important

for choruses now that there is evidence that choruses contain a significant

number of squeaks and barks, which are less than 1s in duration and

potentially add to the information transmitted by the chorus. Information could

potentially be camed in the overall modulation of the chorus, as defined by

the CoFM.

In ternis of overall structure, Schassburger (1987, 1993) defined two

types of choruses, harmonious and discordant. A harmonious chorus is one in

which the howls are uttered in sequence. one over the other, with very iittle

modulation, while a discordant chorus is one in which the howls are uttered in

a discordant manner, with much frequency modulation. Lehner (1 978, 1982)

described the same scenarîo for coyotes with the group howl and the group

yip-howl. In this study, these two foms were not distinguished. All choruses

were discordant, even the spontaneous choruses, which Schassburger

suggested were harmonious. It would be better to Say that choruses follow a

graded continuum of frequency modulation which may have something to do

with the combination of vocal types within and rnay Vary with the arousal level

of the pack.

Choruses have been described as beginning with one animal uttering

one or several solo howls, which are followed by howls uttered by one or

more pack members (Joslin, 1967). Choruses in this study were not always

started in this fashion. In one response, the initial vocalization was a growl,

uttered by a subdominant male. Squeaks and howls of other pack members

quickly followed this. Some researchers have alluded to other vocal types

being incorporated into the chorus. For example, Mech (1 966), Murie (1 944,

Joslin (1 967), Hamngton 8 Mech (1978a) and Tooze (1 987) made mention of

barks occumng dunng choruses. In none of these studies however were the

barks associated with the choruses and the possibiiity of the combination of

barks and howls together in a chorus was not completely explored. Typically,

vocal types other than howls are oniy made reference to in association with

the chorus but not being a part of the chorus. This is akin to suggesting that

the message in a piece of music that is meant for an orchestra is conveyed

solely by the piano and that the sounds carried by the other instruments,

while associated with the music, are somehow removed, or extraneous to the

main message. The combination of sounds conveys the entire message.

Behaviorally choruses have been described as highly contagious

events within the pack (Crisler, 1958), ones which are accompanied by much

face nuniing and tail wagging (Hanlngton & Mech, 1978a). The data from

this study were consistent with these descriptions. Wolves would typically

rally around each other, face nuule, and tail wag. This was observed most

often at the beginning of the chorus and after the chorus had ended. The

behavior of the wolves during these close contact associations may serve to

further stimulate the pack into responding and perhaps the vocal types

associated with these behaviors serve to unify and/ or enhance the motivation

of pack members. For example, if these raliying sessions are accompanied by

a large number of growls and barks, perhaps the resulting chorus will be more

aggressive (lower frequency) as the motivation of the pack rnembers

becomes more aggressive.

Regardless of what the wolves were doing prior to stimulus broadcast

(usually sleeping, resting, eating, sometimes playing or greeting), upon

hearing the stimulus, the wolves always reacted the same way. They would

look up, stand, ears erect, tails dom, and stare for varying arnounts of time in

the direction of the stimulus broadcast. The prior activaies did not seem to

have any effect on the resulting chorus. Responses uttered when the wolves

had been sleeping prior to stimulus broadcast were as modulated, etc, as

when the wolves were more active (greeting, playing). The response would

typically begin before the end of the stimulus. Perhaps the wolves were

listening for the first few howls of the stimulus to gauge the motivation,

distance, or perhaps the identities or the nurnber of animals vocalizing. Once

the chorus had begun, the wolves would sometimes stand on available

structures (better vantage point), and they would keep their relative poslions

without a great deal of movement. other than vocalizing. When the wolves

stopped vocalizing. they would look in the direction of the stimulus broadcast

before resurning pre-chorus behaviors, such as eating or sleeping. This

staring suggests that the wolves remember the contexts under which they

started the chorus and that perhaps they are still attending to the original

stimulus.

Vocal signals camed over long distances must contain al1 the

necessary information without the aid of visual and olfactory cues. For this

reason, it is theorized that these vocalizations should be structurally

stereotypic to minimize the ambiguity of the message that structural variability

introduces. This stereotypy of long distance vocalizations was observed for

arboreal dwelling primates (example, Cercocebus albigena) where visual

cues are absent between groups because of the forested habitat (Waser,

1977; Waser & Waser, 1982). Wolves living predominantly in forested

habitats occupy territories that covei up to several hundred square kilometen.

This limits the use of visual cues when conveying information between packs.

According to Waseis (1977) theory then, the chorus of wolves, which is the

main mode of transmitting information over long distances between packs,

should be fairly stereotypic in structure, that is, the vocalization should not be

variable stnicturally in terms of frequency modulations and vocal composition.

This, however, is not the case: choruses of wolves are indeed quite variable

in both frequency modulation and vocal composition. The question is why are

choruses so complex if the primary message is to be tmnsmitted over long

distances? The answer may lie in the nature of the vocal types contained

within the chorus and to whom the information is directed. The chorus

contains both short distance and long distance vocal types indicating that a

large portion of the information is meant for intra-pack communication rather

than to a neighboring pack.

Vocal Composition of Choruses

The choruses of wolves have been described as long distance

vocalizations, which play a significant role in interpack communication,

primarily functioning in tenitory defense. The chonis may provide information

on pack identity, location, motivation and, potentially, pack size. It's been

suggested that the frequency and the frequency modulations contained within

the howls are the primary structural components that cany this information. I

propose that the combination of the associated vocal types also assists in

conveying the information to neighboring packs.

The vocal type known as the howl was the most numerous in the

choruses, with a mean of 56% of the total number of vocalizations counted. In

this study, three foms of the howl were identified. These three foms were the

solo howl, the breaking howl and the woa-woa howl. The f o m described as

the solo howl made up the largest number of the howls in the choruses

(96%). These howls were relatively flat (CoFM=3.2%), low f requency (5 1 2 Hz)

and long duration (1.78 s). When the solo howls were cornpared structurally

to both the breaking howls and woa-woa howls, they were found to be higher

frequency and longer duration. According to Morton's motivational-structural

niles, this would indicate that the solo howl is not as aggressive a sound as

either the breaking howl or the woa-woa howl. This is not consistent with

findings by Hamngton and Mech (1978a) who observed that the mean

fundamental frequency for solo howls was lower than that for breaking howls.

However, the sample size for this present study was only n=l breaking howl,

which was not representative of the vocalization. Morton (1977) suggested

that animal sounds follow a graded continuum whereby lower frequency

sounds are more aggressive and high frequency sounds, at the opposite end

of the continuum are more Yriendly'.

Woa-woa howls were not rnuch lower in frequency than the solo howls,

yet their structure was very different. Rather than a flat howl, these howls

consisted of short chevron shaped howls in sequence with virtually no

temporal separation. They tended to occur near the middle of the chorus and

added to the overall modulation of the chorus. Woa-woa howls were

described by Tooze (1987) in conjunction with an animal that had been

isolated from its pack mates. This study shows it in another context, the

chorus. It'ç been suggested that these howls contribute to a form of Beau

Geste effect as proposed by Krebs (1977), whereby animals exaggerate their

apparent numbers to rivals, in this case, to other wolf packs (Hamngton,

1989). Overall, the howls in the study were somewhat shorter than those

previously reported. It's been reported that the howls of adult wolves fast at

least 3 s (Theberge & Falls, 1967; Hamngton & Mech, 1978a), however the

data from this study showed that the mean duration of howls was less than 2

S. This is consistent with previous work, indicating that howls uttered in

chorus are shorter than howls uttered alone (Joslin, 1967; Hamngton & Mech,

1 978a; Tooze, 1 987).

Squeaks were a large part of al1 C ~ O N S ~ S recorded dunng this study.

They accounted for 3611 1% of al1 chorus vocalizations. Squeaks are high

frequency, short duration vocalizations that function in communication

between pack members. In this study the squeaks were not heard at

distances of 300 m so the theory that they function as short distance

vocalizations is weil founded. If this were correct, why would this vocal type

be so prevalent in choruses, vocalizations that are heard over distances up to

lOKm (Joslin, 1967; Harrington & Mech, 1978a)? Squeaks serve to

communicate between pack members and operate in many contexts; from

adult to pup (Fox, 1971 ; Coscia et. al. 1991 ; Goldman et. al. 1995), pup to

adult (Fox, 1971; Petenon, 1974). adult to adult (Harrington & Mech, 1978a).

In al1 cases, these contexts are non-aggressive. It has also been observed

that during choruses. Young, or subordinate animals will often squeak and try

to lick the face of more dominant animals (Harrington & Mech, 1978a). This

was obsewed in this study also. Choruses were typically accompanied by

squeaking, face nunling, tail wagging, which sometimes lasted throughout

the entire chorus, atthough these behaviorç were most often obsewed at the

beginning of choruses and after the chorus had ended. This vocal type may

serve to rally the wolves together and involve the whole pack in the chorus.

Barks were uttered in 10 of the 17 choruses recorded during the study.

Behaviorally the bark is considered an aggressive sound that may serve to

attract attention toward the vocalizing animal (Bekoff, 1974), who is often

visually conspicuous (Harrington & Mech, 1978a). Structurally barks bear the

physical characteristics that make them localizable (Harrington & Mech,

1978a). These vocalizations are short duration, low frequency with a sharp

onset and a broad spectrurn. Konishi (1973) indicated that short bursts of

energy covering a broad spectnim should be easy to localize. If barks are

easily localizable their inclusion in choruses could indicate the general area of

their territory to neighboring packs and lone, dispersing wolves, thereby

lessening the chances of an encounter. This would be beneficial since most

encounters between wolf packs result in interpack strife (Mech, 1994). It is of

interest to note that barks were not uttered in the spontaneous choruses. In

the two spontaneous chonises recorded dunng the study, only Iiowls and

squeaks were heard. This would be consistent wÏth the previous theory on the

importance of localizability of the chorus. A spontaneous chorus occur~

without any apparent stimuli and is therefore not necessarily directed toward

any particular listener, thereby removing the necessity of including information

on location. Many more natural chonises would have to be analyzed for vocal

composition to make any concrete conclusions however.

Growls were uttered in 8 of the 17 choruses recorded during the study.

Growls were only heard in choruses that alço contained b a h . This vocal

type has been described as a deep, course sound (Harrington & Mech,

1978a) which functions primarily in the contexts of waming, threat, defense,

attack and dominance (Fentress, 1967; Fox, 1971 ; Field, 1978; Hamngton &

Mech, 1978a; Schassburger, 1987, 1993). These are the same contexts that

are associated with the bark vocal type. It would be logical therefore for

growls to be heard in choruses that also contain barks. However, growls are

not heard at distances that normally separate wolf packs in the wild. In this

study, growls were not heard from the 300 m that separated the pack from the

audio recording equipment. The growls were only accurately recorded on the

video recordings made within several meters from the pack. If this is the case,

and growls are not heard by neighboring wolf packs, what is their role during

a chorus? They are likely used to comrnunicate between pack members

during the chorus and may serve to communicate the state of arousal of the

dominant animals to the rest of the pack. Morton (1977) suggested that

animal vocalizations foilow motivational-structuml rules whereby low

frequency sounds convey aggressive motivations M i l e higher frequency

sounds convey more Yriendly' motivations. The growls may serve to provide

an intemal (within pack) stimulus which motivates the pack to respond more

aggressively (with lower frequency howls and barks) to neighboring packs if

they are perceived as a threat. Morton (1977) also suggested that long-

distance vocal signals might communicate subtle changes in the motivationai

state of social, group-living animals that communicate between groups. In this

way the growl may affect the overall state of arousal within the pack and this

change in motivation may be conveyed to neighboring packs in the chorus.

The combination of vocal types within a chorus could potentially cany

information. This has been proposed for coyotes (Canis latrans) whereby the

combination of two or several sound types would cany specific information

over long distances (McCarley, 1978). It has been suggested that the

frequency, du ration, and overall frequency modulation of choruses cany the

relevant information, but perhaps the vocal composition of choruses is equally

important.

Effectiveness of Stimuli

The stimuli for this study were successful at eliciting vocal responses

from the study packs. These stimuli were artlicially created from human howl

imitations and manipulated to create stimuli that varied on a graded

continuum of duration, frequency modulation and the number of individuals

participating in the stimuli. In this study however, two of the stimuli were less

successful at eliciting vocal responses than the rest. Stimulus 1 and Stimulus

2, both representing one wolf, failed to elicit responses in 3 of 6

presentations. Several studies have utilized live human howling representing

one wolf howling (recent examples include Harrington & Mech, 1979, 1983;

Harrington, 1987, 1989; Tooze, 1987; Fuller & Sarnpson. 1988). The stimuli in

some of these studies had variable success in eliciting responses.

Fuller and Sampson (1988) used human howls (after Harrington &

Mach, 1982) to elicit vocal responses from wolves to conduct a census of wolf

density in a given area. The stimuli, which consisted of one person emitting a

sequence of three howls, were presented to wolves on 22 nightç, at a mean

of 7.5-sites/ night, for a total of 165 presentations. Vocal responses were

elicited for 11 of these presentations. In this case, this method was not highly

effective at estimating the number of wolves in the area. Harrington and

Mech (1982) had more success with their study yet found that stimuli that

represented two wolves howling, rather than stimuli that represented one

wolf, were better at eliciting responses. It was suggested however that stimuli

of single howlers be utilized to census wolf numbers because small wolf ,

packs responded less to stimuli representing two animals than they did to

single howls. The use of single howler stimuli would thereby lessen the

difference in reply rate between small and large packs (there was no data on

the number of animals in a srnall pack versus a large pack). The present

study showed that stimuli representing 2 or 5 wolves were more effective at

elicling responses than stimuli representing 1 wolf, even for the smallest pack

in the study, the pack at the International Wolf Center. that consisted of four

animals. Depending on the nature of the studies, perhaps the use of pack

stimuli would be more successful at eliciting responses than the previously

used single animal stimuli.

Vocal Mimicry

Vocal mimicry is reportedly a common occurrence in animal signaling

systems (Zahavi & Zahavi, 1997). Jays (Garru/us glandanus), for example,

are able to mimic a telephone ring, sending unsuspecting people to answer it.

Also, many have heard the panot (Psittacidae sp.) mimic human speech in

seemingly appropriate contexts (or people mimicking the parrot mimicking

them). One suggested function of mimicking is to convince a listener that the

vocal communication is being addressed to it specifically (Hultsch & Todt,

1986 in Zahavi & Zahavi, 1997). In many bird species, such as indigo

buntings (Passenna cyanea), it was observed that the birds mhic the songs

(called song-matching) of their neighbors (Payne, 1983). Perhaps wolves,

wben responding to the vocalizations of conspecifics, mimic some aspects of

the chorus.

The data frorn this study were mildly suggestive of vocal mimicry, in

ternis of overall duration and frequency modulation of the chorus. As the

duration and CoFM of the stimuli increased, there was a trend toward

increased duration and frequency modulation of the elicited choruses. This

could indicate that wolves respond with choruses that closely match that of

the stimulus, perhaps to indicate to the stimulus pack that 1 is responding

directly to thern and not to another pack (or a spontaneous chorus). Further

studies on this should concentrate more on the frequency modulation

because wolf packs frequently begin their responses to chonises before the

stimulus chorus is terminated which suggests that they do not attend

specifically to the overall duration of the stimulus.

It would be interesting to discover whether or not wolves mimic the

choruses of their conspecific neighbors and if so, it would be equally

interesting to discover whether they also mimic the choruses of syrnpatric

species such as coyotes. Birds frequently mimic the songs of sympatric

species. One theory is that by mimicking the territorial or aggressive

vocalizations of competing species, birds can deter their competitors from

shared resources (Harcus, 1977). Both wolves and coyotes are territorial and

both employ characteristic vocalkation used in the defense of these territories

(wolves chorus and coyotes group yip-howl (McCarley, 1975; Lehner, 1978;

Lehner, 1982). Where the species are sympatric coyotes typically inhabit the

areas that are at the boundaries of resident wolf pack temtories (Fuller &

Keith, 1 981 ). Coyotes inhabit these areas, known as 'buffer zones', because

wolves are rare there, and wolves often kill coyotes they catch. Perhaps

coyotes are considered rivals for space and food resources, and by mirnicking

the coyote group yip-howl, wolves can deter them from occupying a certain

area.

Conclusions

The wolf group vocalization referred to as the chorus howl has

historically been described as a form of howl, one which is uttered by two or

more pack mernbers vocalizing together. While this group vocalization does

contain howls, it also contains squeaks, barks, growls and bark-howls. For

this reason the vocalization should not be classified as a howl. The chonis

howl should be referred to simply as the "chorus" in the future and be given its

own category as a separate vocal type. The data also provided evidence that

the vocal types contained in the chorus corresponded to the vocal types

previously described for the woM, suggesting that the combination of these

vocal types within the chorus may provide the information that the chorus

carries both within the pack and between packs. The combination of vocal

types within a chorus might also be a function of vocal mirnicry. Data was

mildly suggestive vocal mimicry, or vocal imitation, whereby wolves rnirnic the

duration and frequency modulation of the stimulus chorus.

Directions for Future Research

This study provided evidence that the chorus vocalizations of wolves

contain several of the vocal types previously described for the species. The

data was also mildly suggestive of vocal mimicking , whereby chorus

responses mimic the duration and frequency modulation of the stimulus. The

evidence however does not elucidate the kind of information canied in the

chonis. It has been hypothesized that chonises may provide information

about pack size to neighboring packs and dispersing wolves looking to settle

new tenitories (Mech, 1970). A study by Hamngton (1989) suggested that

choruses might not cany such information on pack size. He obseived that

during the course of his study, that involved human howling at wolf packs and

recording responses, that humans could not accurately count the number of

wolves participating in a chorus, even between groups of two to three wolves.

Spectrographically, larger groups (4 to 12 wolves) were indistinguishable from

one another. These findings would suggest that wolves howl to exaggerate

the apparent nurnber of individuals howling. This would be particularfy useful

for smaller packs. There is evidence that pack encounters are influenced by

pack size. wlh larger packs prevailing (Mech, 1966; Mech & Freznel, 1971 ;

Harrington, 1989). Any information about pack size contained within the

chorus could therefore determine the outcome of the encounter. Because

encounters between wolf packs seldom occur, it was predicted that the

chorus might facilitate the avoidance. In this way, Harrington (1989)

suggested that the chorus of wolves might provide the first mammalian

exarnple of Krebs' (1 977) Beau Geste effect. This effect was suggested for

birds, whereby resident birds on a territory had large Song repertoires to

exaggerate the number of birds in an area and discourage nonresident birds

from settling. A study similar to that conducted here could be undertaken to

see if wolves exaggerate their numbers in the chorus to ward off potential

intniders or if they mimic the chorus of the intruder to acknowledge its

presence. In such a study, particular ernphasis should be placed on furllier

analyzing the woa-woa howl and its effect on the overall frequency

modulation of choruses.

Observations from this study suggested that at distances that typically

separate woif packs in the wild, squeaks and growls contained within the

chorus are not heard. A study in which the position of the recording

equiprnent was taken into account could provide information on the distances

at which the vocal types can be heard. This would ascertain what vocal types

in the chorus are used to cany information to other packs (between packs)

and which vocal types provide information within the pack during a chorus.

This information could potentially lead to better understanding intra-pack

interactions during a chorus. The more information available about the

physical parameters of the chorus, the more will be understood about the

functions of these vocalizations, which will give us a better understanding of

the wolf vocal communication system, and subsequently about wolf behavior.

Ao~endix 1. Formula used to calculate the coefficient of frequency modulation

(CoFM).

CoFM = 1 f(t) - f(t+l) 1 + [ t - (t + 1 )] + mean frequency * 100%

f(t)= fundamental frequency at time t

n= number of sample points

Appendix 1.

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